Advances in data storage technology have provided for ever-increasing storage capability in devices such as DVD-ROMs, optical drives, and disk drives. In hard disk drives, for example, the width of a written data track has decreased due in part to advances in read/write head technology, as well as in reading, writing, and positioning technologies. More narrow data tracks result in higher density drives, which is good for the consumer but creates new challenges for drive manufacturers. As the density of the data increases, the tolerance for error in the position of a drive component such as a read/write head decreases. As the position of such a head relative to a data track becomes more important, so too does the placement of information, such as servo data, that is used to determine the position of a head relative to a data track.
An embodiment of a rotatable disk for use in a data storage device in accordance with the present invention comprises an inner diameter, an outer diameter, and a servo wedge disposed between the inner diameter and the outer diameter. The servo wedge includes a first end, a second end, a preamble field extending from the first end to the second end, and a servo-burst field extending from the first end to the second end. The servo-burst field has a set of servo-bursts forming a chevron angle relative to the preamble field. A burst-frequency of the set of servo-bursts varies between the first end and the second end.
In another embodiment of a rotatable disk for use in a data storage device in accordance with the present invention, the servo-burst field includes two sets of servo-bursts—a first set of servo-bursts and a second set of servo bursts. A burst-frequency of one or both of the first and second sets of servo-bursts varies between the first end and the second end.
An embodiment of a system for use in a data storage device in accordance with the present invention comprises a reference disk including an inner diameter, an outer diameter, and a servo wedge disposed between the inner diameter and the outer diameter. The servo wedge includes a first end, a second end, a preamble field extending from the first end to the second end, and a servo-burst field extending from the first end to the second end. The servo-burst field includes one or more sets of servo-bursts forming a chevron angle relative to the preamble field. A burst-frequency of the set of servo-bursts varies between the first end and the second end. A circuit converts a signal of the servo wedge read by a read/write head so that the signal does not vary between the first end and the second end.
An embodiment of a method in accordance with the present invention comprises providing a reference pattern disposed between an inner diameter and an outer diameter of a disk, the reference pattern including a first end, a second end, and a servo wedge extending from the first end to the second end having a preamble field including digital information arranged circumferentially across the preamble field at a first frequency, and a servo-burst field including a set of servo-bursts arranged across the servo-burst field circumferentially at the first frequency from the first end to a transition region of the disk and arranged at a second frequency from a transition region to the second end. Digital information is sampled from the preamble field with a head. A preamble signal is obtained from the digital information samples from the preamble field. The preamble signal is filtered. The set of servo-bursts of the servo-burst field are sampled with the head. A servo-burst signal is obtained based on the first set of servo-burst samples from the servo-burst field. When the head is positioned between the first end and the transition region, the servo-burst signal is the set of servo-burst samples. When the head is positioned between the transition region and the outer second end, the servo-burst signal is obtained by converting the set of servo-burst samples from the second frequency to a third frequency, filtering the servo-burst samples, and converting the filtered set of servo-burst samples from the third frequency to the first frequency. The servo-burst signal is filtered.